Plenty of thiel fellows have started billion/multi million dollar companies (figma, ethereum, luminar, upstart, etc.), so it seems that $100k had been enough for them.
But was this with the $100k. I am guessing they got chosen by Thiel and then with his connections raised a lot of funding later from someone else. There is no way you can start a successful tech company with just $100k. Things are so expensive. Maybe 100k is good enough for a hobby but you are not going to make a living off that.
Well they seemed to have done it, I know plenty of startup founders that have bootstrapped with less than that.
The stamp of approval from Thiel and his network help of course, and is likely more valuable than the $100k but for a lot of these students it gives enough runway to tinker for 2-3 years before landing product market fit.